AND, OR, XOR, ANDNOT, ORNOT, XORNOT all have the same precedence and so are evaluated from left to right. But, as the manual says:
Left-to-right is, in our opinion, unacceptable as a method of specifying the order of
evaluation. USE PARENTHESES to avoid ambiguity!
IF (A=1 AND B<6) OR (A=2) THEN makes it much clearer.